Dual volume control system for radio receivers



w 9 v H. B. MARTRN 7 2,255,390

. DUAL VOLUME CONTROL SYSTEM FOR RADIO RECEIVERS Filed April 25, 1940406M cam/Wm BREW??? COWWL HNVENTOR III" HERSCHEL 5. MART/N ATTORNEYPatented Sept. 9, 1941 were DUAL VOLUME CONTROL SYSTEM FOR RADIORECEIVERS Herschel B. Martin, Brooklyn, N. Y., assignor to RadioCorporation of America, a corporation of Delaware Application April 25,1940, Serial N 0. 331,501

7 Claims.

This invention relates to a volume control system for a radio receiverand has particularly to do with the provision of a dual control systemwhereby the loud speaker volume may be controlled from either of twopoints remote from one another.

Situations frequently arise where a single radio receiver may beemployed to operate two loud speakers, one in one room and one in adifferent room. In order that an occupant of either room may control thevolume to suit his own taste, it is, of course, a matter of greatconvenience to have a volume control device within easy reach. To beable to control the volume from either of two points is somewhat likebeing able to light and extinguish a stairway lamp from either anupstairs or a downstairs switch. However, the problem of controlling thevolume of a radio receiver is more complicated than the lighting switchsystem just mentioned.

It is an object of my invention to provide a volume control deviceoperable from either a local or a remote point.

it is another object of my invention to provide a dual control for avolume device in combination with an automatic volume control device,such that a desirable sound level may be obtained in a given loudspeaker connected with a radio receiver.

It is another object of my invention to provide a radio receiver circuitarrangement including a sensitivity control device operable from eitherof two separated positions.

Other objects and advantages of my invention will be made apparent inthe description to follow.

The invention is best illustrated by a single circuit diagram as shownin the accompanying drawing.

The drawing shows a radio receiver comprising a radio frequencyamplifier and mixer I feel with incoming modulated carrier frequencyenergy as collected on the antenna 2. The output from the RF amplifierand mixer l is preferably delivered to an intermediate frequencyamplifier 3 the output from which is then passed to a second detectorand audio frequency amplifier a portion of the energy being diverted,however, for use in an automatic gain control device.

The output from the last stage in the audio frequency amplifier t may beimpressed across the primary of a transformer 5 the secondary of thistransformer being in circuit between the of these loud speakers 6 mayconveniently be located adjacent the receiver, while the other loudspeaker l is located at any suitable remote point, say, in a differentroom as indicated by the dot and dash line W which might represent awall between the two rooms.

By grounding one terminal of each of the voice coils in the loudspeakers 6 and 1 respectively, the other terminals of these loudspeakers may be connected to the two terminals of the secondary in thetransformer 5. A series circuit is, therefore, normally closed throughthe transformer secondary and the two loud speaker coils. However, it ispossible to short-circuit either of the loud speaker coils and to usethe other loud speaker, if so desired. Each of the loud speakers is,therefore, provided with a short-circuiting switch 8 for by-passing theloud speaker circuit to ground. It is convenient to operate the switch 8in conjunction with the movable tap (9 or ill, as the case may be) of apotentiometer. Combination controls of a type similar to this are wellknown, as, for instance, where an onand-oft switch is operable from avolume control knob on a radio receiver. In this case the movableelement 9 on potentiometer H is provided with an insulation lug i2which, when moved to the uppermost position, causes the local switch 8to close for short-circuiting the loud speaker 6. A similar lug I2 isprovided on the movable element ID of the remote poteniometer foractuating the remote switch 8 to close the same when the lug i2 israised to its uppermost position.

Potentiometer H has its two terminals respectively connected tocorresponding terminals of the potentiometer I3. Potentiometer H ispreferably one of high ohmic value, whereas potentiometer 13 has arelatively low ohmic value. The positions of these potentiometers mightbe reversed; but if so, the operating procedure will be slightlydifferent from that which will now be described.

The purpose of potentiometers H and i3 is to enable an operator ateither the local control point or the remote control point to adjust thebias voltage which is to be applied tothe grids of the super-controltubes in the radio frequency amplifier and in the intermediate frequencyamplifier respectively. The adjustment of the grid bias voltageinfluences the sensitivity of the amplifiers in such manner that, in theabsence of a carrier wave to which the receiver is tuned, substantiallyall 10W level noise eifects may be voice coils of two loud speakers 3and 1. One suppressed and will not reach the loud speakers.

An operating potential source M is provided having a plate voltagesection and a negative grid biasing section, the connection between thetwo sections being grounded. From the negative terminal of the source Ita conductor is taken to a point E5 in a circuit connection between thelower terminals of the potentiometers II and IS. A resistor i6 isinterposed between point l5 and potentiometer ii. The upper terminals ofpotentiometers ii and I3 are interconnected and they also have aresistive ground connection through resistor IS. The purpose ofresistors l5 and i8 will be hereinafter explained.

The potentiometer tap 9 is connected to the grid biasing circuit L?which feeds a bias voltage to the various grids of the tubes whose gainand sensitivity is to be controlled.

In addition to the manual volume control device I preferably employ anautomatic gain control system of any well known type. For the sake ofsimplicity, I have shown such an AVC system as including a dioderectifier 20 the electrodes of which are in circuit with the secondaryof a transformer 23. This transformer is supplied with a portion of theoutput energy from the intermediate frequency amplifier 3. Other meansof diversion of this energy are, of course, well known in the, art as bycapacitive coupling means, for example. In response to variations in thecarrier energy from the I. F. amplifier the diode rectifier 23 is causedto supply the necessary negative bias for maintainin a desired outputlevel from the amplifiers. Such a level is preferably one which willsuppress background noises when no signal is present. A suitable timeconstant device consisting of resistor 22 and capacitor 23 is providedfor slowing up the action of the AVG system. The grid bias lead I9 isconnected to one terminal of the resistor 22 remote from the cathode ofthe diode rectifier 20.

Two single-pole double-throw switches 24 and 25 respectively areprovided, one at the local control point and the other at the remotecontrol point. The switch blade of switch 24 is connected to the movabletap 9. The switch blade of switch 25 is connected to the movable tap IDat the remote station. Conductor 25 interconnects switch points A and Cof the respective switches; likewise conductor 2'! interconnects switchpoints B and D.

The mode of operation of my invention is as follows:

Consider first that the listener is stationed at the local control pointand desires to receive a communication by listening to the loud speaker6. Being unable to reach the remote volume control potentiometer IE3, hethrows the switch 24 into whichever position will produce an opencircuit between the switch blades 24 and 25. That is to say, bothconductors 26 and 21 will be deadended. Under this condition theposition of the potentiometer tap i0 is of no concern to the operator.He then adjusts the volume level of the receiver by means of theadjustable tap 9 which is within easy reach. This tap supplies a morenegative biasing voltage if it is in a lower position and a morepositive biasing voltage if it is raised to an upper position.

Assume now that it is desired to listen to a communication as receivedon the loud speaker circuit to be established across one or the other ofthe conductors 25 and 21. If, therefore, switch 24 happens to rest onits contact A, switch 25 will be moved to contact 0. On the other hand,if switch 24 happens to be resting on contact B, then switch 25 must beset to contact D. Under these conditions the lower resistance value ofthe potentiometer l3 predominates in its control effect over the controleffect of the high resistance potentiometer H, no matter what thesetting of the latter may be. It will thus be seen that the operator ateither the local point or the remote point is able to adjust the volumeof the incoming signals to suit his own taste. When, however, it isdesired that the loud speaker near the operator should be shut off, itis only necessary to move the potentiometer tap to the extreme upperposition, when the insulation lug i 2 resses against the contact spring8 for shortcircuiting the associated loud speaker coil. This operationdoes not appreciably affect reception on the other loud speaker, which,of course, may be kept going for standby reception requirements.

The function of resistors l6 and I8 is to limit the current fiow throughpotentiometer taps 9 and II! when they are interconnected by one or theother of conductors 2G and 2'! and when one tap is moved to a positionof extreme negative voltage value while the other tap is moved to aposition approximating ground potential. Shortcircuiting of thepotentiometer connections is thus avoided.

Various modifications of the circuit arrangement may be made by thoseskilled in the art without departing from the spirit of the invention.For example, it is quite possible to employ dynamic loud speakers havingfield coils which are energized by the main power supply source.Furthermore, it is possible to combine the diode detector tube 20 asused for automatic volume control with components of a detector tubeserving to supply the audio frequency amplifiers. This variation has notbeen shown since it was thought desirable to indicate clearly a typicalAVC device per se in connection with the grid biasing circuit l9.

My invention has been found particularly use-- ful in connection withmarine radio systems where, for example, the radio apparatus is locatedin one cabin, say, the radio operators cabin, a remote loud speakerbeing provided in the wheel house. On small vessels, however, it will beunderstood that the radio apparatus may be installed in the wheel houseand the remote loud speaker may be placed in the captains cabin. Infact, any suitable arrangement of the local and remote control stationson board the vessel may, of coul'se, be provided.

I claim:

1. A dual volume control system for a radio receiver comprising meansincluding a direct current grid biasing source for establishing a normalgain ratio in certain amplifier stages of said receiver, a voltagedivider of relatively high ohmic value having its terminals resistivelyconnected across the terminals of said source and having a movable tapconnected to the grids of said amplifier stages, a voltage divider ofrelatively low ohmic value having its terminals connected tocorresponding terminals of the first said voltage divider and having amovable tap, the two said voltage dividers being respectively located atseparate control stations, a singlepole-double-throw switch at eachcontrol station. B64 11 said switch having a movable contact memberconnected to an adjacent one of said movable taps on the voltagedividers, and conductors interconnecting corresponding stationarycontact members of the two said switches, said switches constitutingmeans for at times interconnecting the movable taps of said voltagedividers.

2. A system in accordance with claim 1 and having an automatic volumecontrol device fed with energy from said amplifier stages and arrangedto vary the bias potential applied to said grids.

3. In a dual volume control system for a radio receiver, the method ofadjusting the normal gain and sensitivity of its amplifier stages fromeither of two separated control stations which comprises adjustablydividing a grid bias voltage through a path of relatively high ohmicvalue at one of said control stations, at times controlling the gain insaid amplifier stages in accordance with said voltage division, and atother times adjustably dividing said grid bias voltage through a path ofrelatively low ohmic value at the other of said control stations whilesimultaneously controlling the gain in said amplifier stagessubstantially in accordance with the last said voltage division.

4. In a dual volume controlsystem for a radio receiver, the methodaccording to claim 3 and including the step of additionally controllingthe gain in said amplifier stages in dependence upon variations in theoutput level of said stages.

5. In a radio receiving system an audio-output circuit comprising twoseries-connected loud speakers located at separated stations,shortcircuiting means for silencing either of said speakers, a volumecontrol device having a relatively Wide range of ohmic values located atone of said stations, a volume control device having a relatively narrowrange of ohmic values located at the other of said stations, means forselectively rendering either of said volume control devices effective toadjust the normal gain and sensitivity of certain amplifiers in saidreceiving system, and manipulative means at each station common to theshort-circuiting means and the volume control device thereat.

6. A local-and-remote volume control device for adjusting the gain incertain radio frequency and intermediate frequency amplifier stages of aradio receiver, said device comprising a constant current sourcearranged to supply a suitable negative bias potential to the grids withrespect to the cathodes of the discharge tubes in said stages, twoseparated potentiometers each having an adjustable tap arranged to feedsaid bias potential to said grids and having terminals resistivelyconnected across said constant current source, one of saidpotentiometers being of higher ohmic value than the other, and switchingmeans adjacent each of said potentiometers for rendering the tap on theadjacent potentiometer effective to adjust the value of the biaspotential applied to said grids, and for effectively disabling the otherpotentiometer.

7. A device in accordance with claim 6 and in combination with twoseparated loud speakers, the same being series-connected in the outputcircuit of said radio receiver, and means including two short circuitingswitches each appropriately operable in conjunction with a respectiveone of said potentiometer taps, when the latter is moved to an extremeposition, whereby a selected one of said loud speakers is silenced.

HERSCI-IEL B. MARTIN.

